1. Field of the Invention
This invention relates to a combination of dye coupling and dye transfer process for preparing a pre-press proof of original artwork using color print paper wherein the dyes of the film are brought into substantial color compliance insofar as contaminants are concerned, the color is fully corrected and the tonal range is equivalent to that of the yellow, cyan and magenta process inks used in producing a lithographic reproduction of the artwork.
The present process permits preparation of a pre-press color proof on photographic color paper developed in dye coupler developer wherein dye transfer colors in a separate operation are combined with the print film dyes to accomplish a hue match with the hue of each process ink color used to produce the original artwork on a printing press. By use of halftone color separations made on an electronic color scanner (or a halftone process color camera), pre-press color proofs employing color print paper may be prepared utilizing the color corrected halftone separation negatives and positives.
2. Description of the Prior Art
It has long been the practice in the lithographic field to provide pre-press proofs before preparing plates for printing. The proofs permit the printer to preview his final product before going to the time and expense of etching the press plates which are difficult and often impossible to alter or revise. Furthermore, all corrections necessary insofar as color balance, color correction and compensation for hue errors in the process inks may be made before the plates are prepared and placed on the press for final mass printing. It is often desirable in the printing trade to furnish the purchaser an exact sample of what the finished printed product will look like for approval before actually printing the job.
In the art to which my invention relates, it is both customary and desirable to provide pre-press proofs from an electronic color separation scanner (or camera) set of halftones separations before preparing plates for printing using the same halftone negatives and positives which will be used to make the printing plates. One reason for requiring pre-press proofs is that it permits the craftsman printer to have a preview of his final product made from his color scanner separation halftones and also permits him to make any corrections on his halftone negatives and positives prior to producing the plates for printing.
Electronic color separation scanners split a beam of light into red, green and blue components. The scanner produces halftone negatives (and/or positives) which are not only color corrected but also function as color separations to prepare plates for printing with yellow, magenta and cyan process inks. The present invention is functional to produce pre-press color proofs from color print paper utilizing halftone color separations which are produced by an electronic scanner or process color camera.
Various processes have been proposed in the past for producing pre-press proofs from halftone separation positives and/or negatives. By way of example, the E. I. DuPont de Nemours Company of Wilmington, Del., has developed a pre-press proofing process called "Cromalin" which utilizes powdered pigment toners. While this process is satisfactory in many respects, Cromalin requires the user to purchase and employ various types of expensive equipment. Further, this equipment requires the use of costly materials and highly trained operators. A health hazard can exist as powdered pigments are dusted onto a photopolymer base and pollute the air in the confined processing area which must be air conditioned to a constant temperature of 72.degree. and 50% R.H.
In like manner and further by way of example, the Minnesota Mining and Manufacturing Company of Minneapolis, Minn., has developed a pre-press proofing process utilizing halftone separation negatives called "Color Key" which results in the production of three overlay layers of colored plastic sheets. This company also produces a pre-press process designated "Transfer Key". Both of these systems use halftone separation negatives (or positives) and require the purchase and use of toned or colored overlay sensitized plastic sheets corresponding to the four process colors which are supposed to match the inks to be used in printing. In practice, however, these sheets usually do not sufficiently correspond to the actual ink color hues. With regard to the "Color Key" process, the use of three or four different plastic sheet overlays is required, one overlay from each of the four separation negatives (or positives), possibly resulting in distortion of the proof.
Eastman Kodak promoted a pre-press color proofing process utilizing color print paper but no compensation was provided for extended tone range or color differences between the process inks and inherent errors in the print paper dyes as compared with the process ink hue errors. The process is described in an Eastman Publication No. 118 issued in 1965.
A more recent example of the prior art is a process offered by the Keuffel & Esser Company of Morristown, N.J., called "Spectra" which also utilizes powder color pigment toners. This process is generally similar to the above-described "Cromalin" process and is subject generally to the same objections and criticisms.